Process for manufacturing prehardened asphalt solid compositions



MEDOC .si .55230 ml D. T. ROGERS ETAL 3,281,256 PROCESS FORMANUFACTURING PREHARDENED ASPHALT SOLID COMPOSITIONS f 3 Sheets-Sheet llnvemors Potent A'rorney ooo 0.o .o Q Q @2m ommmrm Nmmmw mwoom -w Nmmmwmom 03m?. om ...o :EEE mwoom Ommwmfw Oct. 25, 1966 Filed March 29, 1963All :lo .E m @24m .mme l* I2-INH Naousd Dlworfh T. Rogers John C.Mundcly Oct. 25, 1966 I D T, ROGERS ETAL 3,281,256

PROCESS FOR MANUFACTURING PREHARDENED ASPHALT SOLID COMPOSITIONS FiledMarch 29, 1963 5 Sheets-Sheet 2 EFFECT OF HEATING IN AIR PRIOR T0COMPACTION N. J. SANDY CLAY I- II"/ FLUX A ASPHALT MIXED AT 350 F. UNDERNITROGEN COMPRESSIVE STRENGTH psi WET 7 DAYS 2000 HOURS HEATED AT 400 F.

Dilwonh T. Ro ers John C. Mundo? IHVEUIOIS Oct. 25, 1966 Filed March 29,1965 COMPRESSIVE STRENGTH, p si D. T. ROGERS AraTAl. 3,281,256 PROCESSFOR MANUFACTURING PREIIARDENED ASPHALT n SOLID COMPOSITIONS 5Sheets-Sheet 3 EFFECT OF PRE-HARDENING ASPHALT IN SOIL-ASPHALT MIXTUREN. J. SANDY CLAY-I' IO% BINDER GRADE ASPHALT BRICKS COMPACTED AT 75 F.CURED I6 HOURS AT 400 F.

WET 7 DAYS HOURS HEATED IN AIR AT 400 F.

Dilworth T. Rogers John C. Mundoy W@ QW Inventors Potent Attorney UnitedStates Patent O 3,281,256 PROCESS FOR MANUFACTURING PREHARDENED ASPHALTSOLID COMPOSITIONS Dilworth T. Rogers, Summit, and John C. Munday,Cranford, NJ., assignors to Esso Research and Engineering Company, acorporation of Delaware Filed Mar. 29, 1963, Ser. No. 268,862

7 Claims. (Cl. 106-281) The present invention is a continuation-in-partof Serial No. 25 6,666 filed February 6, 1963, entitled Improved AsphaltSolid Compositions and Process of Manufacture,

Inventors: Dilworth T. Rogers and John C. Munday,.

which, in turn, is a continuation-in-part of Serial No. 178,038 filedMarch 7, 1962, entitled Stabilized Asphalt Solid Compositions andProcess of Manufacture, Inventors: Dilworth T. Rogers and John C.tMunday. Both said S.N. 256,666 and said S.N. 178,038 are now abandoned.

The present invention is concerned with prehardened solid compositionsstabilized with petroleum residua and with a process of manufacture ofthese compositions and with shaped articles of manufacture comprisingthese cornpositions. The invention is particularly conerned Withimproved asphalt-stabilized soil and aggregate compositions that haveenhanced dry and Wet compressive strength, superior tensile and fiexuralstrengths, and relatively low water absorption properties. In accordancewith the present invention a high quality, very strong composition isobtained by mixing the asphalt and soil, and then precuring orprehardening the asphalt-soil mixture prior to compaction and curing.

The stabilization of soil and other solids employing petroleum bindersparticularly for use in the construction field has not enjoyedappreciable commercial success. A very limited number of homes has beenbuilt, mainly in the Western part of the United States, in which sandyclay-type soils in conjunction with asphalt 4have been used .to formbuilding blocks. In making these blocks, the asphalt was applied to thesoil as a Water emulsion of an asphalt cutback solution in a naphtha.The mixture was then hand-tamped generally in wooden molds, and theblocks sun-cured for several Weeks. The asphalt functioned mainly as aWaterproofing agent rather than as a binder, since the asphalt increasedthe Wet strength of the `soil but did not appreciably -increase drystrength. In this process, it was considered essential to Wet the soilwith Water before mixing it with the asphalt cutback, or to use anasphalt Water emulsion. The Water deiiocculated the clay aggregate andserved as a compaction lubricant.

It Was found that building blocks produced by this prior art method `andthe composition t-hereof gave maximum u-nconned wet compressivestrengths at about 3 to 8 Wt. percent asphalt, depending upon the ltypeof soil used, but failed to approach the compressive and tensilestrength of commercially available concrete blocks and brick. Despitetheir low unit strength, these materials were of some limited use inarid or semi-arid regions in the form of thick, solid blocks Whereeconomic factors favored their use in certain types of construction.These blocks were wholly unsuitable in other geographical regions Wherethere was a significant variation in humidity or Where these buildingmaterials would contact moisture. Thus, beside very low compressive andtensile strength necessitating the use of thick solid blocks foradequate strength, the prior art asphalt-stabilized soil compositionscould not be used in home construction, even in solid block form, Wherethere Was water Contact or a variation in the humidity of the air,Without a subsequent exterior coating. Thus, these prior art materialscould not be employed, for example, below grade or at footing levels. Afurther disadvantage of these prior art materials Was the poor adhesioncharacteristics of exterior linishes such as paint, mortar, stucco andthe like to the exterior surface of the blocks. The blocks apparentlyexpanded and contracted in response to small changes in the humidity ofthe air, resulting in extensive cracking and peeling of exteriorcoatings.

There has now been discovered a stabilized composition composed ofcritical quantities of subdivided solids and petroleum residua, and aprocess for stabilizing solids, which composition and process avoid manyof the disadvantages of the prior art and provide, for example, as-

phalt-stabilized aggregate and soil compositions of enhanced dry and Wetcompressive strength. In a-ccordance with a specic adaptation of thepresent invention, a critical quantity of asphalt is used in conjunctionwith soil of certain particle-size distribution and is compressed within'a critical range of its theoretical'l00% density. The compressed solidis t-hen heat-treated under specic condition-s `to produce a highquality product suitable as a building material such as blocks, bricks,tile, board, pipe and the like.

Thus, in accordan-ce with the present invention, 8 to 30% by Weight ofthe asphalt is mixed with the subdivided solid. The mixture is thenprehardened by heating preferably in air and the prehardened mixtiue isthen compressed to a density of about to 98% based upon the theoreticaldensity. The compressed product is then cured at a temperature in therange from about 300 to 500 F. for a time period of from about 4 to `80hours. 4

The binder employed in the present invention comprises that family ofmaterials commonly referred to as asphalts, such as natural or petroleumresidua of thermoplastic solid or semi-solid consistency at ambienttemperatures, normally of brown to black cementitious material in which.the predominating constituents are bitumens. The bituminous material tobe used may be selected from a Wide variety of natural and industrialproducts. For instance, various natural asphalts may be used such asnatural Trinidad, gilsonite, Grahamite and Cuban asphalts. Petroleumasphalts suitable for the purposes of this invention include thoseasphalts obtained from California crude, from tar sands, Venezuelan orlMexican petroleum asphalt, or lMiddle East or a Mid-Continent airblownoil and the like, -or combinations thereof. -Petroleum asphalts alsoinclude those `asphalts derived from hydrocarbon feed stocks such asbitumen, asphaltic residua obtained in a petroleum rening process suchas those obtained by the vacuum distillation of petroleum hydrocarboncrude oils, the solvent deasphalting of crude residuum fractions, tarryproducts from the chemical rening such as oxidation of high molecularWeight hydrocarbons, those asphalts obtained from hydrogenated coalproducts, the asphaltic material obtained in the thermal or catalyticcracking of petroleum to obtain gasoline or other light fractions or anycombination of these materials.

Petroleum asphalts are generally prepared from petroleum residual oilsobtained by the distillation of an asphaltic or semi-asphaltic crude oilor thermal tar or by the fluxing of harder residual asphalts with heavypetroleum distillates. Such residual oils are high boiling liquids orsemi-solids which may have softening points from about 32 F. to about120 F. and are generally characterized by speciiic gravities rangingfrom about 0.85 to about 1.07 -at 77 F. Other properties of suchresidual oils, normally termed asphalt bases or asphalt fluxes, may varyto a considerable extent depending upon the particular crude oil fromwhich they are derived. Asphalts prepared from residual oils such asthose set forth above may be classified as either straight reducedasphalts or as yoxidized asphalts. Straight reduced asphalts areproduced by the steam distillation, vacuum distillation, blending orsolvent deasphalting of residual oils. These operations remove asignificant quantity of the lower boiling, more volatile materialpresent in the residual oils and result in Va product having a softeningpoint between about 100 and about 170 F., although higher softeningpoints can be obtained by more extensive treatment. Oxidized asphalts.are produced by contacting a residual oil with air or a similaroxidizing agent, alone or in the presence of an oxidizing catalyst vsuchas ferric chloride, phosphorus pentoxide or the like. The oxidationprocess serves to dehydrogenate certain constituents of the asphalt,leading to the evolution of water and some carbon dioxide. Oilyconstituents are thus converted into resins and resins are convertedinto asphaltenes. Very little oil is removed during the oxidationope-ration. The penetration and dnctility properties of oxidizedasphalts are generally somewhat higher for a given softening point thanare those of the straight reduced products. Both straight reducedasphalts and oxidized asphalts are useful in the invention.

Although the petroleum asphalts are preferred, other suitable bituminousmaterial would include coal tar, wood tar, and pitches from variousindustrial processes. The invention can also be successfully practicedWith chemically modified asphalts such as halogenated, e.g. chlorinatedor sulfurzed or phosphosulfurized asphalts, as well as asphalts treatedwith epoxides or haloepoxides like ethylene oxide and epichlorohydfrin,or with silane halides, nitrobenzene, chlorinated aliphatics such ascarbon tetrachloride and halohydrocarbons such as methylene chloride andthe like. Additionally, the asphalts can be mixed with minor amounts,e.g. 1 to 10 wt. percent, of other natural and synthetic thermoplasticsand thermosetting materials like rubbers, resins, polymers andelastomers, of an oily, resinous, or rubbery nature. Nonlimitingexamples of suitable materials include polyolefins, polypropylene,polyethylene, polyisobutylene, polymers from steam-cracked naphthas andthe like; natural or synthetic rubber-like butyl rubber, halogenatedbutyl rubber, polydienes like polybutadiene, elastomeric copolymers ofstyrene and butadiene, copolymers of ethylene and propylene and thelike; epoxy resins; polyalkylene oxides; natural and synthetic waxes;polyvinyl acetates; phenol aldehyde condensation products; and the likeIand combinations thereof.

Furthermore, in a modication wherein the asphalt is chemically modifiedby reaction with liquid reagents, for example, CC14, the reagent liquidcan often be used as the asphalt solvent, whereupon the desired reactionoccurs before, during or after the compaction of the soilasphalt outbackmixtures, or during lor after the curing step, or the reaction may occurcontinuously during both iinishing process steps.

Satisfactory asphalts, for example, are those designated in the trade asuxes, binders, and various oxidized asphalts. Data on some typicalsuitable asphalts are shown below:

softening Fenetration Asphalt Point, F. at 77 Flux A 75 300 Binder C 11385-100 Oxidized Asphalt 1 ISO-200 24 Oxidized Asphalt 2 20G-235 18 orpetroleum, iron ore, diatomaceous earths, clays, soil, silt, coal,asbestos, glass fibers, quartz, carbonate rocks, volcanic ash, and thelike Vand any combination thereof.

Thus, a Wide variety of solids can be used in conjunction with theasphalt binder to form high strength structures. In general, mineralsare the preferred solids especially those which have well dened crystalshapes and in particular those crystals which are readily compacted tolow voids-content structures. For example, kaolinite, chlorite, talc,mica, specular hematite which crystallize as plates or discs are readilycompacted with lasphalt to produce high strength structures. Asbestos,which has a fibrous structure and attapulgite which crystallize asneedles are less readily compacted.

As is well known, iinely divided solids are more readily compacted togive nonporous structures than coarse.

Clays and clay soils are examples of finely divided solids panding claysare those which swell in the presence of water or other small polarmolecules, and include the montmorillonites (bentonites), vermiculite,and openend illite. Although these clays with asphalt have high drystrength they disintegrate in the presence of water. For use in thepresence of water the soil also should not contain appreciable amountsof organic matter or watersoluble salts.

In order to waterproof clay soils with asphalt it is necessary to coverthe particles with a thin layer of asphalt. Since the surface area ofnely divided solids is high it -is not unexpected that larger amounts ofasphalt would be needed to provide a protective layer on highclay-content soils. For economic reasons therefore it is desirable touse relatively low clay content soils in asphaltsoil block manufacture.A very satisfactory soil is one which contains -about 20-25% clay, theremainder being silt and sand. With this soil 842% asphalt by weight onthe soil will provide high strength and adequate Water repellancy. Itwill be obvious that sandy, silty, and clayey soils can be bleu-ded toachieve the desired particle size distribution.

With some soils and minerals it is possible to obtain high strength withlittle or no clay or finely-divided particles (below 5u) present. Inthese, as mentioned previously, the coarse particles are present ascrystals of nearly equi-dimensional size (plates, discs, prisms, etc.)which are easily compacted to low void content structures. When thecoarser particles are not of this type, as found lin sand and somesilts, the strength of the asphalt soil blocks will be somewhat lowerbut may be adequate for applications where high loads will not be:applied such as in one-story dwellings.

The particle size of soils is ordinarily determined by ASTM MethodD422-54T. In this procedure particle size is calculated from the rate ofsettling in a water suspension. Although clay soils form agglomeratesand aggregates of the primary soil particles they are largely broken upby water. It is thus possible to have a soil which appears to be verycoarse on the basis of a dry screen analysis but which shows a high claycontent in the ASTM D422-54T grain size analysis. On mixing the soilwith :asphalt these agglomerates or aggregates are partially permeatedby asphalt, and to some extent they are disintegrated into ner particleswhich are coated by asphalt. Coverage is not complete, however, and oneobtains a nonuniform structure which may have low strength and highwater sensitivity. It is essential therefore that the largeragglomerates be broken up by light grinding or other means approachingas a limit the same state of subdivision as indicated by ASTM D422-54Tbefore mixing with the asphalt.

Overall, soils in which kaolin is the chief clay constituent arepreferred for block making. Not only is kaolin of the proper crystalshape for easy compaction but it is readily wetted by :asphalt and theasphalt is not as easily displaced by water as with some other clays.There is some evidence also that agglomerates and aggregates of kaolinare broken up during simple mixing with :asphalt and accordingly theamount of preliminary crushing is reduced and coverage is more complete.

FIGURE 1 shows the particle size distribution of various soils whichhave been used successfully in the process of the invention. It will benoted that clay content 0005 mm.) ranges up to 70%. Generally, desirablesoils contain from to 60% clay, with 20% to 40% clay preferred. Amongthe soils which have been found to be useful are Sayreville sandy clay,NJ. red soil, Houston black clay, Lakeland fine sand, Ruston loamy sand,Cecil coarse sandy loam, Cecil fine sandy loam, Marion loam, Neshorningsilt loam, Chester silt ioam, Lakeland fine sand, Nigerian latterite,Georgia kaolin, etc. Although the soils named above do not contain muchgravel (diameter more than 2 mm., equivalent to 10 mesh), soilscontaining gravel or to which gravel has been added can be employed.

The asphalt can be incorporated with the subdivided solid material as asolvent outback, using a volatile organic outback solvent such aspetroleum naphtha or other solvent boiling in the range of about 175 F.to 600 F., e.g. 200 F. to 400 F. The cutback solvent should preferablybe one that is suiciently volatile to be substantially volatilizedduring the selected curing step, i.e., a solvent having a boiling-pointof less than 600 F. or advantageously less than 400 F. Suitable asphaltconcentrations in the cutback solution are from 30 to 90 wt. percentasphalt, e.g. 50 to 75%. Preferably, the Furol viscosity at thetemperature at which the outback is applied should be 100 or lless, e.g.20 to 100 Funol. Suitable cutback solvents thus include, but are notlimited to, hydrocarbons such tas toluene, benzene, xylene, Varsol, VW &P naphtha, halohydrocarbons such as carbon tetrachloride and methylenedichloride, or any combinations thereof. Whatever the solvent, it shouldbe substantially removed from the asphalt-solid mixture prior tocompaction, as disclosed in the parent application, Serial No. 178,038.

The asphalt can also be incorporated with the subdivided sollid while inthe molten state and this is generally l the preferred method. Thetemperature of the asphalt at the time of mixing should be such that theviscosity is sufficiently low that good mixing is achieved and the solidparticles are uniformly coated. Suitable asphalt viscosities are in therange of about 2O Ito 100 Furol, corresponding to mixing temperaturesfrom about 275 F. in the case of soft asphalts such as fluxes, to350-450 F. in the case of harder asphalts such as binders and oxidizedasphalts. In carrying out the hot-mixing operation, the solid isgenerally prehearted and charged to the mixer, and the molten asphalt isthen pumped in. It is usually sufficient to introduce the asphalt as alow pressure spray, although atomized or foamed yasphalt can be used.Various commercial mixers are suitable, such as the type of paddle millknown as .a pug mill.

Generally, it is preferable to mix the `asphalt cutback or the moltenasphalt wi-th solid that is relatively dry, having not more than l to 2%moisture. When solid containing considerable water is employed, it ispreferable to dry the solid-asphalt mixture to a fairly low watercontent prior to compaction. If this precaution is observed, emulsiedasphalt cutbacks can `be employed in the process of the invention. Theamount of asphalt employed 'is in the range from about 8% lto 30% byweight, based on the solid. Generally, 'the amount employed is in therange from about 10% to 20%.

The development of high strength materials from finely divided Isolidsand residua (asphalts) depends to a marked extent on high temperaturecuring, e.g. 300 to 500 F. The time of curing depends on the temperaturelevel, the higher Ithe temperature the shorter the time needed. Ingeneral, the curing conditions to produce blocks which retain theirstrength in the presence of water and which do not labsorb water areless severe than -those required to produ-ce high dry strength.

The principal mechanism involved in the formation of high strengthmaterials from solids and asphalt appears to be oxidation of the asphaltalthough the evolution of volatile material is also involved to someextent. The volatile material may be present in the original asphalt orsubsequently produced by cracking and oxidation.

That oxidation is the chief mechanism is shown by comparing the resultsof curing in air versus nitrogen. In the latter case, with clay soil andasphalt, the compressive strength was less than one-half of those curedin air.

To develop high strength during curing, the compacted solid-asphaltstructure should have sufficient porosity to permit the diffusion ofoxygen into the interior of the structure and to permit the egress ofvolatile materials without disrupting the binder (asphalt) films. Thesolid particles however must `be sufficiently close together so that thegreater part ofthe binder is present as a very thin, nearly-continuousphase if high ystrength is to be developed on curing. Thus if there isinsufficient binder to cover most of the solid particles 'with very thinfilms and if oompaction is not carried to the point where the solids arebrought in close proximity, low strength, especially in the presence ofwater, will result. On the other hand, if an excess of asphalt ispresent, thick films will be formed and l-ow strength will result oncuring, .regardless of the degree of compaction, Aft low densities thestrength of the structure would not be expected to be much greater thanthat of asphalt by itself. A't high densities diffusion of oxygen intothe interior of the strucure and even into the interi-or of the thickbinder films is retarded and more significantly the evolution ofvolatile materials is impeded. The latter effect results in severecracking during curing and produces both deformation land low strength.

In order to designate a suitable range of density (degree of compaction)for the development of high strength an expression Percent ofTheoretical Density has been formulated which is defined as follows:

Percent of theoretical densityzpercent of Ithe density the solid-#binderwould have if there were no voids in the compacted structure.

Percent of theor. dern-Z29 With sandy clay soils containing about 20 to25% clay 5p. particle size) and 9 to 12% -by Weight asphalt, the desiredpercentage of theoretical density is usually within the range 88 to 98%,the exaot level depending upon factors such as the concentration ofasphalt, curling conditions, andthe size and shape of the article beingmolded.

To achieve the advantages of the invention, the asphaltsolid mixtureshould be compacted to a density in the range from about to 98% of Ithetheoretical density, a more preferred range being from about f -to 95%.In many cases, maximum strength is developed in a still narrower range,such as `88 to 92%. The optimum percent theoretical density varies wit-ha number of factors,

such as asphalt concentration, .compaction temperature, presence ofsolvent at the time of compaction, curing conditions, `and the size 4andshape of the article being molded. For example, with sandy clay soilscontaining about 20 to 25% clay 5ft particle size) and 10to 12 wt.percent asphalt, the optimum density is usually in the rrange from about88 -to 94% theoretical density, while with 9% asphalt the yoptimum maybe higher, such as about 96%. Also, whereas the optimum may be about 92%in the case of 1.28" diameter x 3 high -briquettes, it may be about 88%in the case of 8" x 4 x 2.5 bricks. Suitable compaction temperatures.are from 50 to 350 F., preferably from 60 to 200 F.

Thus, in :accordance with the present invention, the asphalt and soilare mixed and prehardened, then cornpacted as described and then cured.

There are a number of advantages for the use of the precuring orprehardening operation. With this method itis possible to use a moreiuid asphalt and thus facilitate mixing with the nely divided solids.Power requirements and mixing time are decreased and more uniformcoating of the solid particles is obtained. Likewise in the preparationof the mixture for compaction the viscosity of the binder can beadjusted so that desired density can be obtained with moderatepressures.

During the precurjng step also some of the volatile fraction of theasphalt and volatile oxidation products are driven off which normallyare evolved during the final curing of the compacted structures. Whenthese volatile materials are escaping from lthe molded or extrudedstructures they tend to break and disrupt the binder film and the resultis lowered strength.

The precuring step also produces a more uniformly cured product. Whenprecuring is not employed the exterior of the structure tends to breakand disrupt the binder lm and the result is lowered strength.

The precuring step also produces a more uniformly cured product. Whenprecuring is not employed -the exterior of the structure tends to beover-cured and the interior under-cured, since the extent of curing islimited by the rate of dilusion of oxygen into the interior of thestructure. By partially preoxidizing during the mixing stage, or atleast prior to compaction, the rate of diffusion of oxygen during curingbecomes less important. Precuring also permits the use of shorter curingtime.

It is preferred that the mixing and prehardening temperature be in therange from about 250 F. to 500 F., time period in the range from aboutone minute to 4 hours. The preferred temperature is in the range fromabout 300 F. to 425 F. for a time period of about two minutes to twohours. Very excellent results are secured at a temperature in the rangeof 350 to 400 F. at a time period from 2 minutes to 40 minutes.

Therefore the invention comprises: (l) Mix hot soil and molten asphaltas described; (2) Preharden the asphalt by heating the soil-asphaltmixture in the presence of air; (3) Compact the mixture into the desiredform; (4) Complete the hardening of the asphalt by curing the formedmaterial at -high temperature.

The invention is further illustrated by the vfollowing examples:

Example 1,-Briquettes were made from a New Jersey sandy clay and 12 wt.percent (based on the clay) of a binder grade asphalt. The asphalt had apenetration of 77 F. of 89 (ASTM D36) and -a softening point of 114 F.(ASTM D5). The sandy clay had the following particle size distribution:

Particle Size, Dia., mm.

In one case the clay and asphalt were mixed hot, in the presence of air,and the mixing in air was continued for one-half hour at 270 F. in orderto preharden the asphalt. In another case the clay was mixed with a50/50 toluene cutback of the asphalt and the toluene was allowed toevaporate at room temperature, thus avoiding prehardening of theasphalt. In each case the soil-asphalt mixture was compacted in a moldat 2340 p.s.i., and` the briquette was then cured for 16 hours at 350 F.

Unconned compressive strength data obtained on the two br-iquettes areshown in the following Table I.

TABLE L EFFECT OF PREHARDENING ON CoMPREssrVE STRENGTH [Briquettescompacted at 75 F. and 2,340 p.s.i., cured 16 hours at 350 F.

The data in Table I show that hardening of the asphalt prior tocompaction increased the briquette compressive strength from 1270 to2110 p.s.i., an increase of 66%.

Example 2.-A New Jersey sandy clay having a particle size distributionsimilar to that of Example 1 was mixed with 11% by weight (based on thesoil) of a soft asphalt known as Flux A. The mixing was carried outunder nitrogen at 350 F. for ve minutes in a Hobart mixer, followingwhich the mixture was cooled under nitrogen to room temperature usingice water to achieve rapid cooling. The nitrogen and the short mixingand cooling time precluded hardening of the asphalt by heat and air. Themixture was then screened through a 20-mesh screen.

Portions of the mixture thus prepared were placed on trays as thinlayers and then put into a 400 F. oven for one, two, four and eighthours. Air was circulated through the oven during the heat treatment.After removal from the oven and cooling to room temperature in air, theheattreated soil-asphalt was then compacted into bricks (7S/s" long x 3%wide). The bricks were cured by heating at 400 F. for 16 hours, and thecompressive strengths of the bricks were detenmined. Details of thecompaction and the resulting brick densities are given in Table II,along with compressive strengths.

TABLE IL EFFECT OF HEATING SOIL-ASPHALT M IXTURES IN AIR [N.J'. sandyclay-H170 Flux A asphalt mixed at 350 F. under nitrogen, cooegoznlernitrogen, compacted at room temperature, cured 16 hours at 0 HeatingCompac- Brick Compres- Brick Time, 'on Density, sive Percent N o. Hrs.at Pressure, g./ce. Strength Change 400 F. p.s.i.

It can be seen from Table II and the corresponding FIG- URE 2 thatsubstantial increases in compressive strength are obtained byprehardening the asphalt before compaction, but after mixing with thesoil, by heating in the presence of air.

The advantage amounts to 25% for one hours heating at 400 F., 54% fortwo hours heating, and 21|% for four hours heating. The criticality ofprehardening is also evident, since eight hours heating resulted in asevere loss in compressive strength. It should be noted that the time=at 400 F. in these experiments was about 15-30 minutes less than therecorded time, due to time required to heat the soil-asphalt mix to 400F.) A further point illustrated by Table 1I is that the compactionpressure increased markedly if prehardening was carried too far.

The compaction pressures shown produced normal bricks of about 2.3inches in height at heating times of zero, one, and two hours. However,even pressures as high `as 7370 p.s.i., approaching the upper safe limitof the machine, failed to produce bricks of normal light and density atfour and at eight hours heating time.

Example 3.-A brick clay obtained trom the area of cooled, screenedthrough a 10 mesh screen, and made into bricks which were then cured andtested as described in Example 3. In some cases, the screenedsoil-asphalt mixture was heated in air at 400 F. for various periods oftime in order to harden the asphalt further prior to com- `pacting intobricks. The results of these experiments are given in Table IV.

TABLE IV INJ. sandy brick clay-HOW? llBlndei- C asphalt mixed at 320 F.for 2 minutes in air coma e at 75 F., cured 16 hours at 400 F.]

Sayreville, NJ., and lconsisting of about 61% sand, 18% silt, and 21%clay, including 10% colloidal clay was heated to 400 F. under anatmosphere of nitrogen in a Hobart mixer. Asphalt of the type describedin Example l, also at 400 F., was added to the clay in the proportion of10 wt. percent based on the clay, the mixer was turned on for iveminutes, and the mix was then cooled with ice and water appliedexternally to the mixing bowl, all under .-a nitrogen atmosphere. Themixture was then screened through 4a 20-mesh screen. The reason forcarrying out the mixing and cooling under an atmosphere of nitrogen wasto avoid oxidative hardening of the asphalt.

Another mixture was lmade using the same ingredients in the sameproportions at the same temperature, but in this -case the mixing wascarried out in air for a total of 18 minutes. The mixture was thenspread out as a l-inch layer on a stone slab and turned over by handuntil cool, whereupon it was screened through la 20-mesh screen. In thiscase the -asphalt in the mix underwent considerable hardening. Todetermine the elfect of further heating in air, portions were placed ina 400 F. oven in thin layers for one hour and for two hours.

The materials described above were compacted into bricks (7%" x 3% x 23).which were then cured by heating in air for 16 hours at 400 F. Thecured bricks were cut in half using a diamond saw and the compressivestrength of the brick-bats was determined, both dry and after soaking inwater for seven days. The results are given in Table III.

The data in Table IV show that exceptionally high compressive strengths,lboth dry and wet, can be produced by the process of the invention.

What is claimed is:

1. A process for the manufacture of a hard bituminous solid compositionwhich comprises the steps of:

(a) mixing soil with about 8 to 30 wt. percent of a Abituminous binderbased on the soil,

(b) prehardening the mixture by heating at a temperature inthe rangefrom about 250 to 400 F. for a time in the range of 1 to 240 minutes ina gaseous atmosphere selected from the group consisting essentially ofair, oxygen and nitrogen,

(c) compressing the mixture to from about 80 to 98% of its theoreticaldensity, and

(d) curing the compressed mixture by heating in air to a temperature inthe range from about 300 to 500 F. for from 4 to 80 hours.

2. A process as defined in claim 1 wherein the amount of binder is inthe range from about 10 to 20 wt. percent and wherein the mixture iscompressed to 85 to 95% of its theoretical density.

3. A process as in claim 1 wherein the mixture is prehardened in air.

4. A process as in claim 1 wherein the mixture is prehardened in oxygen.

5. A process as in claim 1 wherein the mixture is prehardened innitrogen.

6. A process as in claim 1 wherein the solid soil and TABLE IIL-EFFECTOF PREHARDENING ASPHALT IN SOIL-ASPHALT MIXTURE [N.I. sandy clay+10%binder grade asphalt compacted at 75 F., cured 16 hours at 400 F.]

Prehardenin Com ressive Streu th .s.i. Brick Mixing Atmosg Density p g pNo. phere g./ce.

During Subsequently Dry Wet, 7 days Mixing The data in Table III areshown graphically in FIG- URE 3. The data show that prehardening of theasphalt in the mixture, before compaction, results in a substantialincrease in compressive strength. The data also show that excessiveprehardening is highly detrimental to compressive strength.

Example 4. Two hundred pounds of the brick clay was mixed with 20 poundsof the asphalt that was used in Example 3. The mixing was done in a 3cu. ft. pug mill mixer, in air, using a mixing temperature of 320 F, anda mixing time of 2 minutes. Some prehardening of the asphalt occurred inthis operation. The product was binder are mixed at a temperaturebetween 250 and 400 F.

7. A process for the manufacture of a hard bituminous solid compositionwhich comprises the steps of (a) mixing a solid aggregate with 12 wt.percent asphalt based on the aggregate, said asphalt having apenetration at 77 F. of 89 and a softening point of 114 F., said solidaggregate consisting essentially of 58 wt. percent sand having aparticle size of 2.0 to 0.074 mm., 14 wt. percent silt having a particlesize of 0.074 to 0.005 mm., 28 wt. percent clay and 15 wt. percentcolloids,

1 1 v (b) prehardening the mixture by heating in air for 2,900,269 8/1959 about 30 minutes at 270 F., Y I 2,917,395 12/ 1959 (c) compressingthe mixture to between 85 and 95% 2,943,240 6/196() of its theoreticaldensity, and 3,062,672 1 1 1962 (d) curing the compressed mixture byheating in air 5 3,072,593 1/1963 at 350 F. OI' 16 hOul'S. 3,081,1853/1963 References Cited by the Examiner UNITED STATES PATENTS Bauman etal. 106-241 Csanyi 106-122 Martinet 266-43 Kerkhoven et a1 10G-281 Marxet al 260-33.6 Parker 106--218 MORRIS LIEBMAN, Primary Examiner.

ALEXENDER H. BRODMERKEL, Examiner.

J. B. EVANS, Assistant Examiner.

1. A PROCESS FOR THE MANUFACTURE OF A HARD BITUMINOUS SOLID COMPOSITIONWHICH COMPRISES THE STEPS OF: (A) MIXING SOIL WITH ABOUT 8 TO 30 WT.PERCENT OF A BITUMINOUS BINDER BASED ON THE SOIL, (B) PREHARDENING THEMIXTURE BY HEATING AT A TEMPERATURE IN THE RANGE FROM ABOUT 250* TO400*F. FOR A TIME IN THE RANGE OF 1 TO 240 MINUTES IN A GASEOUSATMOSPHERE SELECTED FROM THE GROUP CONSISTING ESSENTIALLY OF AIR, OXYGENAND NITROGEN, (C) COMPRESSING THE MIXTURE TO FROM ABOUT 80 TO 98% OF ITSTHEORECTIAL DENSITY, AND (D) CURING THE COMPRESSED MIXTURE BY HEATING INAIR TO A TEMPERATUTE IN THE RANGE FROM ABOUT 300* TO 500*F. FOR FROM 4TO 80 HOURS.